Science or scientists build a model. If new evidence comes along, the model gets changed. There are several other websites that describe all of this stuff, I will list a couple at the end of this post. Look in an intro, non-science majors textbook and you will probably see a picture like this of the atom.
This model has some good ideas in it, but overall it has some problems. The key and not incorrect points of this model are:. It always has to go back to the Greeks, doesn't it? Well, they did do a lot of stuff. I know they were really scientists but it is still a good place to start. Here is a picture of bust of Democritus.
In real life, he probably had color. Democritus is credited with coming up with the atom. The question was, what would happen if you keep taking something like a tree and breaking into smaller and smaller pieces? Would it always be a piece of a tree? Could you keep breaking it into smaller and smaller pieces? Democritus said that if you keep breaking it down, you would get to a size that could no longer be broken. This would be the indivisible piece. Thus, the atom. I know there is more to the Greeks, but I need a place to start.
I am not going to go into the experimental evidence for Dalton's model of the atom, it's good stuff though. Let me just state what Dalton said:.
Basically, Dalton just expanded on the Greek idea of the atom. An atom is a small things, and there are different masses with different properties. Thomson played with cathode rays.
These are just beams of electrons but cathode ray sounds cooler. By having the beam interact with electric and magnetic fields, Thomson was able to determine the mass to charge ratio for an electron. So, from that he knew that the electron came from the atom, it had a negative charge and a small mass.
Here is the model that he proposed. Thomson took the idea of the atom and tried to incorporate the evidence for the electron. In this model, the electrons are the small things and the rest of the stuff is some positive matter. This is commonly called the plumb pudding model because the electrons are like things in positive pudding. Ernest Rutherford said one day "hey, I think I will shoot some stuff at atoms.
Protons and neutrons are attracted to each other and as a result, there exists the powerful nuclear force. Register Now. Remember Me. Lost Password Lost your password? The protons. The protons Question. Answer: A. The Bohr model can be summarized by the following four principles:. This atomic model is known as the quantum mechanical model of the atom.
Unlike the Bohr model, the quantum mechanical model does not define the exact path of an electron, but rather, predicts the odds of the location of the electron. This model can be portrayed as a nucleus surrounded by an electron cloud.
Where the cloud is most dense, the probability of finding the electron is greatest, and conversely, the electron is less likely to be in a less dense area of the cloud. Thus, this model introduced the concept of sub-energy levels. Until , the atom was believed to be composed of a positively charged nucleus surrounded by negatively charged electrons.
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